Fire detecting thermostat



Nov. 12, 1946. R. P. JAMESON 2,411,093

FIRE DETECTING THERMOSTAT Filed Sept 13, 1944 Patented Nov. 12, 1946 OFFIQE FIRE DETECTING THERMQSTAT Ronald Iurvis Jameson, Christchurch, New Zealand Application September 13, 1944, Serial No. 553,932 In New Zealand September 16, 1943 Claims.

This invention relates to improvements in fire detecting thermostats.

The object of the invention is to provide a device that will be sensitive in detecting incipient outbreaks of fire under varying atmospheric conditions and that can be adjusted by means of a calibrated device to function with any desired minimum rapid rise of temperature.

According hereto, the heat detector is a bimetallic strip coiled in a helix in such a manner that it will rotate in one direction (for example, clockwise) upon being heated, and so arranged as to leave it open to the temperature of the atmosphere of the place where it is mounted. This coil i connected at one end to a rod which is free to rotate with the rotation of the coil as the temperature changes. Attached to this rod is another bi-metallic coil wound in such a manner that it rotates in the opposite direction with its free end acting as a movable electric contact, and so arranged that it is shielded from direct exposure to the atmosphere in order to prevent it from being immediately affected by any rapid rise in temperature, such as would be occasioned by an outbreak of fire.

The free end of the second coil which is capable of acting as a contact is set between two fixed immovable contacts and so that it will make contact with one or the other of these fixed contacts in accordance with certain conditions of temperature, as will be mentioned later. In its normal position, corresponding with the ordinary temperature of the room, it will be in engagement with one of these contacts, but the arrangement is such that upon a rapid rise in temperature it will move from the contact and engage with the other contact and so break and make two electric circuits. When the heat of both bi-metallic coils again stabilizes, the coil-contact moves back to it normal position.

In order that the device may be properly set, a regulator is provided by which the coils are rotated to such a position that the movable contact is brought under tension engagement with its fixed contact and the regulator is then secured in position with fixing screws. Such tension will be released from such contact only upon a predetermined minimum rapid rise of temperature, and such rise of temperature continuing, the movable contact will pass to the other fixed contact.

In one form of the invention, the exposed bimetallic coil is secured. by a screw or the like to the spindle of the regulating wheel; the other end of the exposed coil is secured by a screw to an actuating rod free to rotate within bearings at either end but so arranged as tobe insulated from the regulator wheel or its spindle. The insulation of this actuating rod from the regulator wheel or its spindle is to provide that the electric current must pass through the bi-metallic coils and thus determine that they are in electrical continuity and form part of a circuit. Attached to another portion of the actuating rod is another hi-metallic coil which is shielded from exposure to the atmosphere by the casing of the device; the free end of such second coil forms an electric contact. These coils, when subjected to heat, rotate in opposite directions. The contact being the free end of the shielded coil is normally set in engagement with a fixed contact, thereby ion--- ing part of a normally closed circuit. The tension of the contact engagement is variable by adjustment made at the regulating wheel attached to the exposed coil. In addition to the fixed contact above referred to, another fixed contact on the opposite side of the movable contact is provided to act as a normal open circuit.

When subjected to slow heating, such as normal increases in atmospheric temperature, the exposed coil rotates in an anti-clockwise direction and in doing so rotates the actuating rod and the shielded coil which is attached to it, but as the shielded coil is so arranged as to itself rotate in a clockwise direction, it neutralises the movement of the exposed coil at the free end of the shielded coil and no movement of the movable contact takes place. The purpose of this arrangement is that the thermostat will adjust itself or compensate during normal slow changes of atmospheric temperature. When subjected to a rapid rise of temperature, such as fire, the exposed bimetallic coil rotates in its anti-clockwise direction without a corresponding opposite rotation of the shielded coil and thus the movable contact of the shielded coil is caused to break away from engagement with its fixed contact and breaks the normally closed circuit. Further heating causes the movable contact to engage with the other fixed contact and so to close the normally open circuit. The regulator wheel is provided with calibrated divisions by means of which the tension of the movable contact against the fixed contac is adjustable for the purpose of determining or fixing the minimum rise of temperature which will free the movable contact from engagement with its fixed contact. Such divisions are calibrated to provide easy means of visible adjustment. of the thermostat and these calibrations also provide a ready means of checking adjustmerits.

A fusible link forming part of the normal closed circuit is inserted to limit the compensation to a predetermined temperature and to provide independent means of giving an alarm.

The invention will now be described with the aid of the accompanying drawing, wherein- Figure 1 is a plan view with the end covers 8 and i9 removed.

Figure 2 is a section on the line A-A in Fi ure 1.

Figure 3 paratus.

Figure 4 is an end View from line 3-13 on Figure 3, with the end cover l9 removed.

Figure 5 is an inverted plan of Figure l, and

Figure 6 is a section on the line CC in Figure 5.

Referring now to the drawing, the thermostat comprises a bi-metallic strip I coiled in a helix in such a manner that it will rotate in an anticlockwise direction upon being heated and so mounted as to leave it exposed to the temperature of the atmosphere where the thermostat is mounted. This coil is connected at one end by a screw 3 to a rod 2 which is free to rotate within bearings i and I 2a with the rotation of the coil as the temperature changes. Attached to the rod 2 is another bi-metallic coil 4 wound in such a marmer that on being subjected to heat it rotates in a clockwise direction, i. e., in the opposite direction to that of the coil l, with its free end 5 acting as an electric contact, and so arranged that it is shielded by the walls of the chamber as from direct exposure to the atmosphere in order to prevent the coil 4 from being immediately affected by any rapid rise in temperature, such as would be occasioned by an outbreak of fire. This compensating effect makes the device give an alarm on a rapid rise in temperature, but prevents it from giving an alarm in normal slow changes in atmospheric temperature.

The free end of the second bi-metallic coil which acts as a movable contact is set between two fixed immovable contacts 9 and I8 and so that it will make contact with one or other of these fixed contacts in accordance with certain conditions of temperature, as will be mentioned later. In its normal position corresponding to ordinary atmospheric conditions, it will be in engagement with the contact 9 under tension according to the position of the adjusting wheel l5, which is of insulating material, the casing I6 being also of insulating material. When the thermostat is subjected to a rapid increase of temperature, the coil I, which is exposed, rotates in an anti-clockwise direction causing the rod 2 and the coil 4 to rotate in the same direction and is a sectional elevation of the apthe contact 5 to release its tension against the contact 9 and break away from engagement therewith, thus opening a normally closed electric circuit. Further rapid heating causes the contact 5 to move over to engagement with the contact I 0, closing a normally open electric circuit. When the temperature of both coils again stabilises, the contact 5 moves back to engagement with the contact 9.

If the thermostat is subjected to a slow rise in temperature, such as normal atmospheric changes, both the exposed bi-metal coil and the shielded bi-metal coil are affected thereby and both rotate, but as the shielded coil rotates in an opposite direction (clockwise) no movement of the contact 5 takes place, and in this manner the thermostat compensates to slow changes of temperature and remains equally sensitive to a rapid increase of temperature such as would be occasioned by fire regardless of atmospheric temperature at the time of such fire.

When the thermostat is subjected to a rapid temperature rise, such as fire, the exposed bimetallic coil alone is immediately affected and rotates in its anti-clockwise direction, without a corresponding opposite rotation of the shielded coil 4, and thus the movable contact 5 is caused to break away from engagement with the contact 9 and to engage with the contact it.

With all changes of temperature, whether normal or abnormal, the rod 2 is caused to rotate Within its bearings, thus keeping them free from sluggish action at all times, which might be the tendency were they constantly at rest as a result of accumulated dust or the eifects of corrosive fumes or the like.

The screw 1 provides a means of adjusting the bearing so that there is float or side play for the rod 2 and the pointed ends of the same are resting on the slopes of their respective bearings, thus providing the minimum of frictional resistance to free movement when the rod is rotating. The adjustable bearing 6 provides means of centralising the rod 2 within the hole through the casing at 2 3 and ensures that the said hole can be of the necessary minimum diameter to prevent friction against the rod 2 and/or penetration of dust or insect life into the interior chamber in which the coil 5 and the contacts are housed.

The adjusting disc is provided with calibrated divisions by means of which the tension of the movable contact 5 against the fixed contact 9 is adjustable for the purpose of providing predetermination of the degree of minimum rapid rise in temperature necessary to free the contact 5 from engagement with the contact 9. Such divisions are calibrated to provide easy means of visible adjustment of the thermostat without resort to trial and error methods of adjustment, and also to provide a ready means of checking adjustment.

A fusible link i6 connected at one end to a terminal plate 23 and at the other end to a spindle 14, forms part of the electrical circuit which can be traced as follows: From the terminal plate 9a to the fixed contact 9, movable contact 5, bi-metal coil 4, rod 2 to the screw 3, bi-metal coil I, screw I 3, rod I d, fuse l8, terminal plate 23. The purpose of this fusible link inserted within the circuit is to provide a predetermined maximum temperature at which the above described circuit will break regardless of whether the rise in temperature is slow or fast, the fuse It? being composed of two parts of spring metal joined together with fusible metal and so mounted that upon fusion one part springs away from the other and makes a distinct separation and so gives an alarm.

As described above, a slow rise in temperature, such as a normal rise in atmospheric temperature, will cause the bi-metal coil 4 to rotate in a contrary direction to the bi-metal coil l and thus neutralise the movement of the coil 1 so that no movement of the contact 5 takes place and the fusible link is provided to detect an abnormal slow rise of temperature before a dangerous temperature is reached, such as might be occasioned by a smouldering fire.

After the device is assembled, the thermostat must first be set at zero position, i. e., when the contact 5 engages with the fixed contact 9 without tension. When the contacts are at this position, the adjusting wheel I 5 on the rod Hl'is turned until the arrow pointers 22 (indicating zero position) are in line with the bottom of the projections 25 on the wall of the casing, and in this position the adjusting wheel is secured to the rod M by a screw {5a. The thermostat is now ready for adjustment.

The calibrated divisions 2! on the adjusting wheel correspond to and measure the extent of rotation of the lei-metal coil I for a given number of degrees of heat applied to the said coil.

When the adjusting wheel is set at zero position, as described, any rotation of the adjusting wheel rotates contact 5 in the same direction. For the purposes of detecting a rapid rise in temperature, the adjusting wheel is rotated in the direction in which the moving contact 5 is brought into tension engagement with the contact 5 and then looked at the desired position by the screw 65!). For example, if it is desired to set the thermostat so that the contact 5 will break away from the contact 9 when it is subjected to a minimum rapid rise in temperature of say twenty degrees, the adjusting wheel is turned (in the direction of the contact 9) so that the arrow positions are, say, four divisions away from zero position and locked in that position.

It will be readily understood that the actual rise in temperature required to operate the thermostat at any predetermined setting is determined by the speed of the rise in temperature, this being due to the compensating effect of the coil 4 and, therefore, a minimum rapid rise in temperature is emphasized. The greater the speed of the rise in temperature, the lower the operating temperature within the minimum rise of temperature determined by the setting.

By insulating the rod 2 from the rod l t with an insulating piece 12 (Figure 3), both coils are caused to carry all electric current from the terminal plate 25 to the contact 9 and this, being part of a closed circuit, causes both coils to be under automatic continuity test so that should either coil break as a result of corrosion or other cause, an alarm is given.

The ring 25 is used to secure the bi-metal coil I to the actuating rod 2 by means of the screw 3, while another ring 26 is used to secure the bimetal coil l to the spindle M, and in both cases to complete and maintain the electrical circuit by means of the bi-metal coil i.

A grub screw 2'5 secures the bush 26 to the spindle M, while securing screws 23 are shown at various points and a screw 29 or rivet connects the bi-metal coil l to the actuating rod 2. Standard terminal connections are shown at 33. The coil I is protected over its length by protection ds 32 mounted in brackets or the like 3!, whilst the end covers 8 and iii are secured to the protection rod brackets 3! through the casing it of insulating material by screws 33, such end covers 8 and it also being of insulatin material.

What I claim is:

l. A fire detecting thermostat comprising a support having conical recesses, a rod, a first bi-metaliic coil open to the atmosphere and tending to rotate the rod in one direction on being subjected to heat, an enclosure, a second bi-metallic coil encased from the atmosphere Within said enclosure and tending to rotate said rod in the opposite direction on being subjected to heat, a normally closed circuit contact normally engaged by the free end of the second coil, a normally opened circuit contact, both ends of the rod being conical and mounted in said conical recesses so that on the movement of the first mentioned coil by a sudden increase of temperature the free end of the second coil will break away from engagement with said normally closed circuit contact and engage with said normally open circuit contact and thereby give an alarm of fire.

2. A fire detecting thermostat, comprising a rotatable rod, a bimetallic fire-detector coil fixed at one end and secured to said rod at the other end in such a manner as to rotate the rod in one direction on bein subjected to heat, a second bi-metallic coil rotatable with the rod and having a free end constituting a moving contact, such second bi-metallic coil being arranged so as to rotate itself upon being subjected to heat but in an opposite direction to the first mentioned coil.

3. A fire detecting thermostat as claimed in claim 1, provided with an adjusting wheel, a second rod connecting the first mentioned coil to said adjusting wheel, such adjusting wheel being capable of being rotated and thereby to r0- tate the first mentioned coil, and then secured in position for the purpose of adjusting and determining the sensitivity or" the device to a rapid rise of temperature, the second mentioned rod and wheel being insulated from the first mentioned rod in order to ensure that the electric current will be carried through the coils.

4. A fire detecting thermostat as claimed in claim 1, provided with an adjusting wheel, a second rod connecting the first mentioned coil to said adjusting wheel, such adjusting wheel b ing capable of being rotated and thereby to rotate the first mentioned coil, and then secured in position for the purpose of adjusting and determining the sensitivity of the device to a rapid rise of temperature, the second rod and wheel being insulated from the first mentioned rod in order to ensure that theelectric current will be carried through the coils, and means for making visible measured adjustments for fixing a minimum limit to the rapid rise of temperature at which the apparatus will function.

5. A fire detecting thermostat as claimed in claim 2, provided with an adjusting Wheel, a second rod connecting the first mentioned coil to said adjusting wheel, such adjusting wheel being capable of being rotated and thereby to retate the first mentioned coil, and then secured in position for the purpose of adjusting and determining the sensitivity of the device to a rapid rise of temperature, the second rod and wheel being insulated from the first mentioned rod in order to ensure that the electric current will be carried through the coils, and means for making visible measured adjustments for fixing a minimum limit to the rapid rise of temperature at which the apparatus will function, and having means for fixing a maximum limit of temperature beyond which limit the apparatus will not compensate.

6. A fire detecting thermostat as claimed in claim 2, provided with an adjusting wheel, a second rod connec ing the first mentioned coil to said adjusting wheel, such adjusting Wheel being capable of being rotated and thereby to rotate the first mentioned coil, and then secured in position for the purpose of adjusting and determining the sensitivity or" the device to a rapid rise of temperature, the second rod and. wheel being insulatedfrom the first mentioned rod in order to ensure that the electric current will be carried through the coils, means for making visible adjustments for fixing a minimum limit to the rapid rise of temperature at which the apparatus will function, means for fixing a maximum limit of temperature beyond which limit the apparatus will not compensate, bearings for the first rod, and means for adjusting the bearings and securing the alignment of the first rod thereon.

7. A fire detecting thermostat as claimed in claim 2, provided with an adjusting wheel, a secondrod connecting the first mentioned coil to said adjusting 'wheel, such adjusting wheel being capable of being rotated and thereby to rotate the first mentioned coil, and then secured in position for the purpose of adjusting and determining the sensitivity of the device to a rapid rise of temperature, the second rod and wheel bein insulated from the first mentioned rod in order to ensure that the electric current will be carried through the coils, means for making visible adjustments for fixing a minimum limit to the rapid rise of temperature at which the apclaim 2, in which the adjustment is made by rotating the coil.

10. A fire detecting thermostat as claimed in claim 1, means for adjusting the sensitivity of the device by setting the tension of the contacts in the normally closed circuit, by means of a calibrated device.

RONALD PURVIS JAMESON. 

